The Phase 5 AR-15 Pistol Buffer tube is made from billet aluminum and features an ultra durable nitrile rubber foam pad for comfort. This version of the kit includes a mil-spec castle nut and endplate. The buffer tube is compatible with standard Mil-Spec carbine buffer and springs. The lower slot is machined to accept all mil-spec end plates and sling mounting accessories. The tube is compatible with the SIG SAUER Pistol Stabilizing brace ensuring a nice snug fit for no unwanted brace movement.